One known method of forming hollow articles is to rotate a mould simultaneously about two rotational axes which extend transversely of one another whole moulding material within the mould is in a fluid condition, so that the moulding material is spread entirely over the inside of the mould; on solidification of the moulding material a hollow article is thus provided. The moulding material may be a plastics material, and may be a thermoplastics material rendered fluid by heat. The two rotational axes may extend perpendicularly to one another, and either or both of the rotary motions of the mould may be an oscillatory rotary motion. This method of forming hollow articles is what is meant herein by the term "rotational moulding", and by the term "rotational moulding machine" is meant a machine for performing rotational moulding.
There have been suggested many different constructions of rotational moulding machine, but it is well known to employ a machine construction in which a plurality of mould carriers are mounted at regular angular intervals about a main axis of the machine, the mould carriers being mounted on a rotatable turret which can be indexed step-by-step about the main axis to bring each of the mould carriers in turn to a work station of the machine; for moulding thermoplastics materials the work stations of the machine will generally include a loading/unloading station at which a moulded article can be removed from a mould and a fresh charge of moulding material placed in the mould, at least one heating station at which a mould can be heated to maintain moulding material in the mould in a fluid condition while the material is spread over the inside of the mould, and at least one cooling station at which a mould can be cooled prior to removal of a moulded article therefrom. A machine which comprises a turret mounted for rotation about a vertical main axis is, for example, disclosed in U.S. Pat. No. 3115680 (Soderquist), and machines which comprise a turret mounted for rotation about a horizontal main axis are, for example, disclosed in U.K. pat. specification No. 1352701 (Orme) and West German Offenlegungsschrift No. 2223117 (Thermovox).
In a machine comprising a plurality of mould carriers mounted on a turret, drive means must be provided for rotation of the moulds on mould carriers which are stationed at some of the work stations of the machine, but provision made for a mould to be stationary, to permit handling of the mould by an operator, when its mould carrier is at a loading/unloading station of the machine. In the machines disclosed in U.S. Pat. Nos. 3,115,680 and 2,223,117, this is readily provided for by having separate drive units at each of the work stations where rotation of the mould is required, engagement and disengagement of the drive means being effected simply by movement of the mould carrier to and from the work station.
However the provision of separate drive units at each work station of the machine means that during indexing movements of the turret the drive means is disengaged, and for this and other reasons it may be preferred to employ a single drive unit with which the mould carriers can be selectively engaged at any position of the turret as required for rotation of a mould. A machine of this latter kind is disclosed in U.K. patent specification No. 1352701, the machine having a single drive unit in the form of two independently driven driving wheels which are mounted for rotation about the main axis of the machine, the machine comprising clutch means whereby drive from the driving wheels to each of the mould carriers can be engaged as required at any position of a mould carrier about the main axis; the clutch means of the machine comprises a plurality of clutch units, one for each mould carrier, which each operate to engage idler wheels between the two driving wheels and two driven wheels of the associated mould carrier for transmission of drive from the driving wheels to the driven wheels for rotation of a mould on the mould carrier. Whilst this construction of machine has proved satisfactory in many circumstances, the complexity of the clutching arrangement, whereby drive to a mould carrier from the drive unit is engaged and disengaged, is generally undesirable.